Statistics.java

//  Statistics.java
//
//  Author:
//       Antonio J. Nebro <antonio@lcc.uma.es>
//       Juan J. Durillo <durillo@lcc.uma.es>
//
//  Copyright (c) 2011 Antonio J. Nebro, Juan J. Durillo
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
// 
//  You should have received a copy of the GNU Lesser General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.

package jmetal.experiments.util;

import java.util.Vector;

/**
 * This class provides methods for computing some statistics
 */
public class Statistics {

    /**
   * Calculates the median of a vector considering the positions indicated by
   * the parameters first and last
   * @param vector
   * @param first index of first position to consider in the vector
   * @param last index of last position to consider in the vector
   * @return The median
   */
  public static Double calculateMedian(Vector vector, int first, int last) {
    double median = 0.0;

    int size = last - first + 1;
    // System.out.println("size: " + size + "first: " + first + " last:  " + last) ;

    if (size % 2 != 0) {
      median = (Double) vector.elementAt(first + size / 2);
    } else {
      median = ((Double) vector.elementAt(first + size / 2 - 1) +
              (Double) vector.elementAt(first + size / 2)) / 2.0;
    }

    return median;
  } // calculatemedian

  /**
   * Calculates the interquartile range (IQR) of a vector of Doubles
   * @param vector
   * @return The IQR
   */
  public static Double calculateIQR(Vector vector) {
    double q3 = 0.0;
    double q1 = 0.0;

    if (vector.size() > 1) { // == 1 implies IQR = 0
      if (vector.size() % 2 != 0) {
        q3 = calculateMedian(vector, vector.size() / 2 + 1, vector.size() - 1);
        q1 = calculateMedian(vector, 0, vector.size() / 2 - 1);
        //System.out.println("Q1: [" + 0 + ", " + (vector.size()/2 - 1) + "] = " + q1) ;
        //System.out.println("Q3: [" + (vector.size()/2+1) + ", " + (vector.size()-1) + "]= " + q3) ;
      } else {
        q3 = calculateMedian(vector, vector.size() / 2, vector.size() - 1);
        q1 = calculateMedian(vector, 0, vector.size() / 2 - 1);
        //System.out.println("Q1: [" + 0 + ", " + (vector.size()/2 - 1) + "] = " + q1) ;
        //System.out.println("Q3: [" + (vector.size()/2) + ", " + (vector.size()-1) + "]= " + q3) ;
      } // else
    } // if

    return q3 - q1;
  } // calculateIQR


}